Message-ID: <4BE3C4C9.60601@uci.cu>
Date: Fri, 07 May 2010 09:44:09 +0200
From: Marcos Ortiz <mlortiz@uci.cu>
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To: Mark Stosberg <mark@summersault.com>
CC: pgsql-performance@postgresql.org
Subject: Re: debugging handle exhaustion and 15 min/ 5mil row delete
References: <20100507093742.20c715b1@summersault.com>
In-Reply-To: <20100507093742.20c715b1@summersault.com>
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El 07/05/2010 15:37, Mark Stosberg escribió:
> Hello,
>
> We've been a satified user of PostgreSQL for several years, and use it
> to power a national pet adoption website: http://www.adoptapet.com/
>
> Recently we've had a regularly-timed middle-of-the-night problem where
> database handles are exhausted for a very brief period.
>
> In tracking it down, I have found that the event seems to correspond to
> a time when a cron script is deleting from a large logging table, but
> I'm not certain if this is the cause or a correlation.
>
> We are deleting about 5 million rows from a time-based logging table
> that is replicated by Slony. We are currently using a single delete
> statement, which takes about 15 minutes to run. There is no RI on the
> table, but the use of Slony means that a trigger call and action is made
> for every row deleted, which causes a corresponding insertion in another
> table so the deletion can be replicated to the slave.
>
> My questions:
>
> - Could this kind of activity lead to an upward spiral in database
>    handle usage?
>
> - Would it be advisable to use several small DELETE statements instead,
>    to delete rows in batches of 1,000. We could use the recipe for this
>    that was posted earlier to this list:
>
>    delete from table where pk in
>      (select pk from table where delete_condition limit X);
>
> Partitions seems attractive here, but aren't easy to use Slony. Perhaps
> once we migrate to PostgreSQL 9.0 and the hot standby feature we can
> consider that.
>
> Thanks for your help!
>
>      Mark
>
>   . . . . . . . . . . . . . . . . . . . . . . . . . . .
>     Mark Stosberg            Principal Developer
>     mark@summersault.com     Summersault, LLC
>     765-939-9301 ext 202     database driven websites
>   . . . . . http://www.summersault.com/ . . . . . . . .
>
>
>
>    
You can use TRUNCATE instead DELETE. TRUNCATE is more efficient and 
faster that DELETE.
Now, we need more information about your system to give you a certain 
solution:
Are you using a RAID controller for you data?
Do you have separated the xlog directory from the data directory?
Which is your Operating System?
Which is you architecture?

Regards